Cumulative Energy Demand Systems
CED systems measure and evaluate the energy consumption of the building. Energy is furnished to buildings to cover needs such as heating, ventilation, air conditioning, water heating, lighting, entertainment and telecommunications. The specification of the energy request is of primary importance as CED systems can refer to just some of the above consumptions (often, just heating and hot water consumption) or can consider all needs without distinction regarding the final use.
CED systems evaluate the energy consumption over a time unit, which generally corresponds to one year. However, monthly or semi-annual evaluations have been proposed (Marszal et al., 2011). Energy consumption for residential buildings in developed countries at middle latitudes assumes values of some hundreds of kilowatt hours per square meter net floor surface per year (kW h/m2 a): for example, heat consumption of traditional European and US buildings is 300 kW h/m2 a on average (Butera, 2010). Referring to traditional buildings, operating energy demand dominates the building CED during the life cycle, being 80% of the total energy consumption (Suzuki and Oka, 1998). A small energy percentage is consumed for material manufacture and transportation, construction and demolition. Consequently, energy saving policies have typically only given attention to operation energy performance (EC, 2003). Energy consumption requirements of new buildings are greatly decreasing under the pressure of more stringent requirements (Figure 1).
Figure 1. Energy requirements for heating in some European building codes over the years (data taken from national regulations)
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In the US, zero energy buildings (or ZEBs) are discussed in the Energy Independence and Security Act (EISA, 2007), whereas the recast of the European Energy Performance of Buildings Directive (EC, 2010) has established that only ZEBs should be built after 2020. A ZEB can be defined as a building with a very high level of energy efficiency, so that the overall annual primary energy consumption is equal to the onsite energy production from renewable energy sources. A universally accepted definition of ZEBs is still lacking (Marszal et al., 2011), and several proposed methodologies for ZEB calculations differ for the metric of the analysis (energy, CO2 emission, costs), the balancing time and the type of energy use considered in the assessment.
As highly efficient buildings are built, the energy needs during construction and demolition processes, together with the embodied energy in construction materials, become relatively more significant. Hernandez and Kenny (2010) have defined the life cycle zero energy building (LC-ZEB) concept for energy consumption equity in a whole life perspective. A life cycle evaluation of energy use implies enlarging time and space boundaries in the assessment (Suzuki and Oka, 1998), and represents the trend for energy based sustainability assessment in the construction sector.
CED systems are a mono-dimensional analysis, which considers the energy flux. Apart from an energy analysis, some researchers have accounted for other measurement units, such as exergy (Tronchin and Fabbri, 2008) or emergy (Pulselli et al., 2007). Exergy is the maximum useful work that brings the system into a heat reservoir equilibrium, whereas emergy is the available solar energy directly and indirectly used in a transformation. These units of measurement are related to thermodynamic principles of resource use, and may be more appropriate than energy to evaluate building consumption (Marszal et al., 2011), although energy data are more common in the literature.
Life Cycle Analysis Systems
Several systems have been developed for the environmental assessment of manufactured products, such as Environmental Risk Assessment (ERA), Material Flow Accounting (MFA), Input–Output Analysis (IOA) and Life Cycle Analysis (LCA). These systems generally break down products and processes into elementary parts. LCA is the most commonly used of the above systems. It divides a building into elementary activities and raw materials to assess the environmental impact over a life cycle from manufacture and transportation to deconstruction and recycling (Seo et al., 2006). LCA is a robust methodology refined on the basis of manufacturing sector experiences. LCA assessments consist of four phases (ISO 14040, 2006): the goal and definition phase, the life cycle inventory, the life cycle impact assessment and the improvement assessment phase. LCA systems allow the comparison of products on the basis of the same functional quality. This describes the quality of a product service as well as its duration, e.g. square meters of a building element with a substitution rate every 50 years. The scientific rigor of LCA is inherent to assessments from cradle to grave phases, although it is limited by uncertainties in collecting data relating to building processes. LCA diffusion in the building sector is limited by a lack of information (Seo et al., 2006). In fact, the specificities of the construction processes require data for every building material in any region. Databases have been created for LCA evaluations and implemented in specifically designed software in several geographic areas: BEES in the US, BOUSTEAD and ENVEST in England, SIMAPRO and Eco-Quantum in the Netherlands, Ecoinvent in Switzerland and GaBi in Germany. However, these databases are only valid for assessments in a specific region. The United Nations Environment Program's Sustainable Buildings and Climate Initiative (UNEP-SBCI) has recently adopted the Common Carbon Metric. This system allows emissions from buildings around the world to be consistently assessed and compared. The assessment reports the Carbon Intensity, which is the evaluation in weight of carbon dioxide equivalent emitted per square meter per year (kg CO2-eq/m2 a). The assessment is mainly based on the operational consumption, but it can be extended to the whole life cycle of the building.
An obstacle for LCA diffusion is its specialist structure: outputs of LCA systems are represented by environmental impacts expressed through chemical substances, which are not easily understood by construction sector actors (Langston and Ding, 2001).
LCA systems assess the environmental paradigm of sustainability without considering social and economic impacts. To fit this limit, some studies relate the disaggregation analysis necessary for an LCA to an evaluation of economic costs. Such an approach is interesting for the building sector, as life cycle cost (LCC) analysis represents a familiar paradigm to construction stakeholders. Combined LCA–LCC can, hence, be useful to evaluate environmental and economic aspects in life terms by assigning a price to chemical elements. For example, BEES and GaBi systems already permit the selection of cost-effective environmentally preferable products.
Total Quality Assessment Systems
TQA systems aim at considering the three aspects of sustainability of buildings: environmental issues such as GHG emission and energy consumption, economic aspects such as investment and equity and social requirements such as accessibility and quality of spaces. The most common TQA systems are the multi-criterion systems. They are greatly increasing the attention for sustainable assessment of buildings, as they are well related to market interests and stakeholders' culture (Newsham et al., 2009). Multi-criterion systems base the evaluation on criteria measured by several parameters, and compare real performances with reference ones. Each criterion has a certain number of available points over total assessment and the overall evaluation of sustainability comes out by summing the results of assessed criteria. A critical aspect of multi-criterion systems is their additional structure, as they assign scores for positively evaluated elements (Hahn, 2008). Multi-criterion systems are generally easy to understand and can be implemented in steps for each criterion. Moreover, a step implementation is allowed during the analysis: in fact, these systems enable the assessment of the building at several stages, from the concept design to the final construction, and can be used during construction too.
Several multi-criterion systems exist to assess building sustainability worldwide. As many are just adaptations of more famous ones to regional level or for specific scopes, only the most adopted systems are considered here. These are BREEAM, LEED, CASBEE, SBTool and Green Globes. Other famous rating systems are the Australian Building Greenhouse Rating (ABGR), the Green Home Evaluation Manual (GHEM), the Chinese Three Star, the US Assessment and Rating System (STARS) and the South African Sustainable Building Assessment Tool (SBAT).
The United Kingdom was the first country to release a multi-criterion system for sustainability assessment before this concept entered into the agenda of international policies with the Rio Conference. The British Building Research Establishment Environmental Assessment Method (BREEAM) was planned at the beginning of the 1990s by the British Research Establishment, and was released in 1993. The system has a large diffusion in the United Kingdom, where almost 10 000 buildings have been certified.1 Since 2009, as a consequence of the worldwide attention garnered by this system, an international version has been released, and currently BREEAM has adapted versions for Canada, Australia and Hong Kong. The system is differentiated for 11 building typologies and its evaluations are expressed as a percentage of successful over total available points: 25% for pass classification, 40% for good, 55% for very good, 70% for excellent, 85% for outstanding. The evaluation categories are management, health and wellbeing, energy, transport, water, materials, land use, ecology, pollution and innovation.
A widely spreading rating system is LEED (Leadership in Energy and Environmental Design), which was released in 1998 by rthe US Green Building Council (GBC).2 This system is currently available for ten building typologies. There are six evaluation categories to obtain the 69 possible points of the standard in version 2: sustainable site (14 points), water efficiency (5), energy and atmosphere (17), material and resources (13), indoor environment quality (15) and innovation and regional specificities (5). LEED points accumulated are divided into the following categories: at least 26 points for certified buildings, 33 for silver, 39 for gold and 52 for platinum. Although released in the US, GBC has been diffused worldwide over the years, and recently the World GBC has opened regional chapters in countries in Europe, Africa, America and Asia. Almost 20 000 buildings are registered for certifications, and current requests for new certifications regard buildings in 110 countries2.
CASBEE (Comprehensive Assessment System for Building Environmental Efficiency)3 is a Japanese rating system developed in 2001, also available in English. CASBEE covers a family of assessment tools based on a life cycle evaluation: pre-design, new construction, existing buildings and renovation. This system is based on the concept of closed ecosystems and considers two assessment categories, building performance and environmental load. Building performance covers criteria such as indoor environment, quality of services and outdoor environment, whereas environmental loads cover criteria such as energy, resources and materials, reuse and reusability, and off-site environment. By relating the previous two main criteria, CASBEE results are presented as a measure of eco-efficiency on a graph with environmental loads on one axis and quality on the other, so that sustainable buildings for CASBEE have the lowest environmental loads and highest quality. Fewer than 100 buildings have been certified with this system, although the number is rapidly increasing.
At the end of the 1990s, the Sustainable Building Council promoted an internationalization of rating systems under the leadership of Natural Resources Canada (NRC). Towards this initiative a common protocol, SBMethod, was developed. Using the general scheme, several countries then proposed national versions of this system, such as Verde in Spain, SBTool PT in Portugal and SBTool CZ in the Czech Republic. In Italy, this protocol was implemented in 2000 as SBTool IT, it was updated in April 2011 and it is now known as ITACA. Moreover, ten Italian regions have adopted modified versions of the system to better cover regional specificities. In 2005, adapting the Canadian version of BREEAM, the Green Building Initiative (GBI) launched a new rating system, known as Green Globes. Criteria of this include project management, site, energy, water, indoor environment, resource, building materials and solid waste.
A critical aspect of multi-criterion systems regards the selection of criteria and weight given to each criterion: in fact, reasons behind choices are not explicit. In this paper, among the aspects through which a comparison of sustainability rating systems could be done, criteria and weights were selected. This shows which aspects of building performance are given more consideration in sustainability assessments. Figure 2 shows weights assigned by the above six systems, grouping the criteria of each into seven main categories. Selection of these categories was based on main sustainability building aspects (Langston and Ding, 2001): site selection, energy efficiency, water efficiency, material and resources, indoor environmental quality, waste and pollution. The category ‘others’ contains criteria that do not fit into the other six categories. When more than one version of the same system existed, the one applicable to new construction was selected. The attribution of each system criterion into previous categories resulted in some difficulties because the system structures were not always easily accessible and criteria among systems did not perfectly overlap. For this reason, the attribution was performed by the author, and then repeated by two sustainability experts to check coherence in attribution of criteria in the seven categories. Credits assigned in the LEED system for low-emitting materials (6 points out of 69) were assigned to the IEQ category; however, they could also be assigned to the waste and pollution category, which in Figure 2 has not received any weight. Management and innovation criteria have been included in the category ‘others’. For example, LEED assigns 7% of its credits to innovations, BREEAM has 15% for construction management and Green Globe has 12.5% for project management. Moreover, in the category ‘others’ there are points given by CASBEE for mitigation and off-site solar energy and by GBTool for the cultural perception of sustainability. The result of the weight comparison among rating systems agrees with similar studies (Fowler and Rauch, 2006, BRE, 2008).
Figure 2. Comparison of the weights assigned by six sustainable rating systems, grouping the respective criteria into seven categories
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It is interesting to note that energy efficiency among assessment systems in Figure 2 is always considered the most important category (weight average among the six systems 25.5%), followed by IEQ (17.7%), waste and pollution (15.9%), sustainable site (13.2%) and material and resources (11.5%). Green Globes assigns a higher percentage of its assessment weight to energy efficiency (36%): this is established by the inclusion of criteria that are not presented in other systems, such as the correct size energy efficient system or energy efficient transportation.
The above averages do not have a rigorous meaning, standard deviations among systems are high and percentages change if other versions of the systems or other assessment systems are considered. However, studies have shown many similarities among sustainability rating systems (Smith et al., 2006). Finally, it should be remembered that evaluation criteria and weights are just one of the ways to compare systems. Fowler and Rauch (2006) compared the above mentioned systems for other properties (applicability, usability, communicability), again finding some similarities. Differences among the systems have led to creation of the Sustainable Building Alliance in order to establish common evaluation categories and to improve comparability among systems in sustainability assessments.
Many studies have discussed the limits of rating systems; however, only limits for weight and criteria are considered here. Unscientific criteria selection has been criticized by both Rumsey and McLellan (2005) and Schendler and Udall (2005). Bower et al. (2006) stated there was a lack of overall life cycle perspective in evaluations. On the same topic, the US National Institute of Standards and Technology (NIST) analyzed the LEED system from an LCA perspective, leading to the conclusion that it is not a reliable sustainability assessment system (Scheuer and Keoleain, 2002).
From Figure 2, it is clear that, in the selection of assessment criteria, environmental aspects in existing systems receive much more attention than economic and social ones (Sev, 2009). Recently, some multi-criterion rating systems more closely related to a TQA have been released. For example, the Deutsche Gesellschaft für Nachhaltiges Bauen (DGNB), available since 2009, aims at evaluating sustainability through the quality of the building: economic aspects emerge explicitly, and, in the category of technical quality, paradigms such as performance, durability and ease of cleaning, as well as dismantling and recycling, are considered. More attention is paid to social aspects than in other rating systems. Finally, functional aspects such as space efficiency, safety, risk of hazardous incidents, handicap accessibility, suitability for conversion, public access, and art and social integration are considered.